1. Field of the Invention
The present invention relates to a coating method for forming a liquid film in fabrication processes for electronic devices, such as liquid crystal display devices and semiconductor devices; a coating apparatus; and a method of forming a film.
2. Description of the Related Art
Fabrication processes for liquid crystal display devices, semiconductor devices, and the like, include steps for forming various types of films. Examples of these films are photosensitive films, such as a photoresist film used in photolithography, alignment films and colored films of color filters used for liquid crystal display devices, and interlayer insulating films used for semiconductor devices.
Conventionally, such films have been made of films of coating solutions (liquid films) which are formed by spin coating. Recently, as one method for forming a liquid film, a die coating method is receiving attention. In the die coating method, a coating head (die head) provided with a slit having an opening of approximately 10 to 100 xcexcm comprising parallel edges of two die blades is used. A coating solution, which is ejected from the slit by a gas compressor, a pump, or the like, is directly applied to a planar substrate, such as a glass substrate or a semiconductor wafer, to form a liquid film. The die coating method is also referred to as a slit coating method or an extrusion coating method.
Methods and apparatuses for die coating (slit coating) are disclosed in Japanese Patent Laid-Open Nos. 10-012710 and 11-090295, for example.
By using the die coating method, the amount of a coating solution used can be significantly reduced in comparison with the conventionally used spin coating method. Also, in the case of a liquid crystal display device using a rectangular substrate, a liquid film can be formed only where required on the substrate.
While the die coating method is suitable for rectangular substrates, such as glass substrates used for liquid crystal display devices and the like, with respect to circular and nonrectangular substrates, such as silicon wafers and recording disks, because of the structure of the coating head for ejecting the coating solution, it is difficult to apply the coating solution only onto the substrates. As will be described below, if application is performed by modifying the shape of a stage for holding a substrate, the coating solution is also applied to the periphery of the stage. When a solvent in the coating solution is vaporized, a solidified material remains on the stage, which may affect a film of the coating solution subsequently ejected from the coating head, resulting in nonuniform thickness, and for example, the formation of stripes.
Additionally, in the conventional coating method, regardless of rectangular substrates or nonrectangular substrates, the liquid film formed has insufficient in-plane uniformity. In particular, nonuniform thickness readily occurs where the thickness of the liquid film on edges of a substrate differs from the thickness of the liquid film in the center of the substrate.
It is an object of the present invention to provide a coating method and to provide a coating apparatus for applying a liquid film, in which the liquid film can be uniformly applied repeatedly.
It is another object of the present invention to provide a coating method, a coating apparatus, and a film-forming method, in which a liquid film or a film having superior in-plane uniformity can be formed on a substrate.
In one aspect of the present invention, in a coating method for forming a film of a coating material on a substrate by supplying the coating material from a coating unit to the substrate held by a stage while the coating unit is moved relative to the stage, the stage including a substrate-holding section and a peripheral section which has a surface higher than that of the substrate-holding section, the coating method includes the steps of mounting the substrate on the substrate-holding section of the stage; forming the film of the coating material so that the coating range extends to the peripheral section; and removing the coating material remaining in the peripheral section by a coating material removing unit after the substrate provided with the film is dismounted from the stage.
In another aspect of the present invention, a coating apparatus includes a stage for holding a substrate, a coating unit for supplying a coating material onto the substrate, and a coating material removing unit. A film of the coating material is formed by supplying the coating material onto the substrate held by the stage while the coating unit and the stage are moved relative to each other. The stage includes a substrate-holding section and a peripheral section which has a surface higher than that of the substrate-holding section, and the coating material removing unit removes the coating material applied to the peripheral section of the stage.
In another aspect of the present invention, a method of forming a film includes a step of applying a film of a coating material to a substrate by the coating method of the present invention and a step of baking the film formed by the coating material.
In another aspect of the present invention, in a coating method as well as in a coating apparatus, while a coating head including a slit comprising at least two parallel blades is moved relative to a stage for holding a substrate, a coating material is ejected from the coating head to form a film of the coating material on the substrate held by the stage. After the substrate is dismounted from the stage, the coating material adhering to the stage is removed by a coating material removing unit, and then coating is performed on a new substrate.
In accordance with the present invention, by removing the coating material adhering to the stage, nonuniform thickness, which may occur in a liquid film subsequently formed, can be avoided.
By applying a liquid film to the substrate so that the peripheral section of the stage, which has a surface having a height close to that of the surface of the substrate to be coated, is also within the coating range, nonuniform thickness on the edge of the substrate can be avoided.
Further objects, features and advantages of the present invention will be apparent from the following description of the preferred embodiments with reference to the attached drawings.